Development of a policy and strategy for controlling infection by Heterobasidion annosum in British forests: a review of supporting research

Abstract

Summary Heterobasidion annosum causes serious root disease in conifers: pines are generally killed but other species, such as Sitka spruce, are more susceptible to decay. In the mid-twentieth century, much of the expanding forest estate in Britain was disease free, but as thinning increased in plantations established over the preceding 30 years, it was expected that stump infection would increase; this in turn was expected to give rise to widespread disease. As a control, mandatory stump treatment using various chemicals, or a biological agent, was introduced throughout the Forestry Commission’s estate in 1960. Since that time inoculation experiments have shown that the risk of infection in Sitka spruce varies from site-to-site and is much lower in crops growing on peaty soils than in those on mineral soils. To help predict future losses, a simulation model was devised to describe the behaviour of disease caused by H. annosum in Sitka spruce. It was used to integrate the results of work described here with those obtained from other experiments and from field observations made over many years. Losses were estimated over one or more rotations under various management regimes. Cost–benefit calculations indicated that treatment of Sitka spruce stumps was not likely to be economically justified on upland sites with peaty soils. As a result, the policy of universal stump protection was revised in 2000, so that treatment of Sitka spruce stumps was discontinued on deeper peats and became discretionary on all peaty soils in areas of high rainfall. Implementation of the policy was challenging since soil maps were not available for many forests, and in areas of high rainfall an intimate mosaic of peat and mineral soils often forms in response to local variations in topography. A stump treatment decision support system was developed based on a comprehensive geographic information system map of mainland Britain. This provides a general evaluation of site hazard for any forest crop based on its location, together with estimates of the disease risks associated with stumps and standing trees of different species. Use of this system was adopted as Forestry Commission policy in England and Scotland in 2007.